Sealing assembly

ABSTRACT

A downhole sealing assembly ( 10 ) includes a sleeve ( 12 ) comprising a swellable medium ( 22 ). The sleeve ( 12 ) is mounted on a base pipe ( 14 ) and defines a flow path ( 18 ) between the sleeve ( 12 ) and the base pipe ( 14 ).

FIELD OF THE INVENTION

The present invention relates to a sealing assembly, and in particular to a downhole sealing assembly incorporating a swellable medium.

BACKGROUND TO THE INVENTION

In the oil and gas exploration and production industry there are many occasions where seals of varying configurations must be established downhole. For example, seals may be required within an annulus defined between, for example, concentric tubulars, between a tubular and a bore wall, or the like. Such seals may be achieved by use of mechanical actuators which physically set, and in some occasions release sealing members at the desired location. However, there are inherent reliability concerns associated with any downhole mechanical assembly in view of the significant difficulties and costs associated with recovering a failed assembly and implementing appropriate remedial measures.

It has been proposed in the art to establish seals in downhole annular locations using materials which swell upon contact with a particular activator, such as water, hydrocarbons or the like. Generally, the swellable material, such as a swelling elastomer, is positioned in an annular space and then subsequently permitted to swell, for example upon contact with ambient fluids, to fill the annular space and establish the necessary seal. However, swellable materials which have been proposed for use in downhole applications swell or expand very slowly and generally require a number of days, often weeks, to complete the swelling process and fill the annular space to establish the required seal. This slow activation period may delay subsequent procedures, which is highly undesirable. Furthermore, a constant desire to carry out downhole operations as quickly as possible may encourage certain procedures to be performed before the seal has sufficiently been established which may inadvertently affect the integrity of the seal.

Further concerns in the oil and gas industry relate to wellbore cementing. In conventional wellbore completions, casing or liner tubing strings are run into a drilled bore and cemented in place to seal the annulus defined between the tubing strings and the bore wall to therefore prevent migration of fluids along the annulus. A conventional cementing process involves pumping an appropriate volume of cement through the tubing string, through a cement shoe mounted on the lower end of the string and ultimately into the annulus. However, the condition of the wellbore may often adversely affect the integrity of the cement seal. For example, mud cake formed on the bore wall from the drilling operation may prevent or at least minimise the adherence of the cement to the bore wall. Additionally, after the cement has cured, micro annuli, cracks or channels may form. For example, thermal expansion cycles of the tubulars may cause cracking of the cement and even separation of the cement from the tubulars and/or the bore wall. Additionally, in-well operations may disturb the cured cement. For example, in conventional cementing operations a proportion of the cement will remain and set within the cement shoe, which must be drilled through if the wellbore is to be advanced. Drilling through the cement shoe in this manner may disturb the cement in the adjacent annulus and therefore adversely affect annulus sealing.

Remedial operations to remedy an ineffective prior cement job include cement squeeze operations which involve pumping additional cement through perforations in the tubing string and into the ineffective cemented annulus to seek to fill the micro annuli and other flow channels. However, cement squeeze operations are time consuming and there is a risk that the subterranean producing formation will be damaged.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a downhole sealing assembly including a sleeve comprising a swellable medium and adapted to be mounted on a base pipe and define a flow path between the sleeve and the base pipe.

Advantageously, in use, the sleeve may be mounted on a base pipe and subsequently run downhole into a bore, and the swellable medium may be activated to swell to provide a seal within the annulus formed between the sleeve and a bore wall. The bore wall may comprise an inner surface of a downhole tubular. Alternatively, or additionally, the bore wall may be defined by an inner wall surface of an open drilled bore. In this arrangement the sealing assembly may be adapted to prevent migration of fluids from the surrounding earth into the wellbore, or alternatively, or additionally the loss of fluids from the wellbore into the surrounding earth.

Beneficially, the present invention permits a seal to be established more rapidly than would be achievable if the swellable medium were mounted directly on the base pipe. That is, the annulus area between the sleeve and the bore wall will be less than the annulus area between the base pipe and bore wall, and as such requires a lower expansion ratio of the swellable medium to establish the seal.

The swellable medium may be adapted to swell during deployment into a bore. Accordingly, permitting the swellable medium to begin the swelling process during deployment shortens the final sealing time once the sealing assembly is located at the required depth. Beneficially, the swellable medium may displace ambient or other fluids present in the wellbore during swelling to establish a seal between the bore wall and the sleeve.

The flow path may be defined between an inner surface of the sleeve and an outer surface of the base pipe.

The flow path may be adapted to permit fluids, such as cement, drilling mud, wellbore fluids or the like to flow therethrough. Accordingly, when the swellable medium has established a seal, as described above, the flow path may permit fluids to bypass said seal.

Additionally, the flow path may be adapted to permit resident or ambient wellbore fluids, such as drilling mud, hydrocarbons, water and the like to be displaced therethrough while the sealing assembly is run in-hole. The flow path may therefore assist to prevent or substantially minimise the occurrence of hydraulic locking, permitting easier running in of the sealing assembly. This arrangement is particularly advantageous where the swellable medium defines an outer diameter or dimension which closely corresponds to the diameter or width of the wellbore, especially where the swellable medium is permitted to swell during running into the wellbore. Providing a sealing assembly of an outer dimension or diameter close to the bore diameter also assists in centralising the base pipe in the bore.

The sealing assembly may be adapted for use in combination with a downhole cementing process. For example, the swellable medium may be activated to establish a seal between the sleeve and a bore wall at a desired location, while the flow path permits cement to bypass said seal to provide conventional annulus cement sealing on either side of the established seal. Accordingly, annulus sealing at the desired location is not dependent on cement making a sufficient bond with the bore wall. Additionally, the sealing assembly may provide additional assurance that sealing integrity will be maintained at the desired location, even when flow channels, micro annuli or the like form within the cement or at the cement/bore wall interface. Furthermore, any movement of the sealing assembly relative to the bore wall after a seal is initially established will be accommodated by further swelling of the swellable medium to thus continually maintain a seal.

The flow path may be adapted to permit cement to cure therein, such that the cement provides a seal across the sealing assembly. Advantageously, the flow channel may provide a relatively clean surface permitting good adherence of the cement. Furthermore, any thermal expansion effects will be experienced by both the base pipe and sleeve, which may be formed of the same material, thus minimising any separation of cement from the surface of the flow path.

In embodiments of the invention the sealing assembly may be adapted to be located at a pre-selected location within a wellbore. For example, the sealing assembly may be adapted to be positioned at a location within a wellbore which extends through geological zones or regions containing fluids, such as water, which are preferably to be prevented from being produced to surface. Accordingly, the sealing assembly may be utilised to provide downhole zonal or regional isolation to assist in preventing migration of fluids between regions. For example, the sealing assembly may be utilised to seek to prevent migration of water from one zone towards an oil or gas-producing zone to minimise the volume of water produced to surface.

The sealing assembly may be adapted to be positioned at a region within a wellbore which exhibits undesirable geological properties. For example, particularly porous regions may absorb a significant volume of fluids from the wellbore. Such porous regions, conventionally termed thief regions, may absorb, for example, uncured cement from the wellbore, resulting in incomplete annulus cement sealing. The sealing assembly of the present invention may therefore be utilised to isolate such regions from the wellbore while allowing fluid bypass.

Furthermore, the sealing assembly may be adapted for use in wellbores which extend through relatively weak rock structures, to thus ensure that sufficient sealing and wellbore support may be established.

The sealing assembly may be adapted for use in regions within a wellbore where in-well operations are known to adversely affect the annulus sealing integrity of conventional cement. For example, the sealing assembly may be utilised adjacent, in combination with or part of a cement shoe.

The pre-selected location may be determined by conventional techniques, such as open hole logging or the like. For example, properties of the wellbore may be determined by wireline logging, for example, after the wellbore has been formed or alternatively during drilling of the wellbore using logging while drilling techniques.

The base pipe may comprise a downhole tubular such as a casing tubular, liner tubular, drilling tubular, drilling collar, cement shoe, coiled tubing or the like, or any suitable combination thereof. The base pipe may be of a conventional size, such as a full size 9.14 m (30 feet) pipe section, or a reduced size 4.57 m (15 feet) pup-joint pipe section. The base pipe may be adapted to define or be coupled to and form part of a tubing string to be run downhole into a bore.

The swellable medium may be adapted to swell by volumetric expansion thereof. Alternatively, or additionally, the swellable medium may be adapted to swell by inflation thereof. In embodiments of the invention the swellable medium may be adapted to swell upon exposure to an activator. The swellable medium may be adapted to be activated by a chemical activator, thermodynamic activator, fluid dynamic activator, or the like, or any suitable combination thereof. For example, the swellable medium may be adapted to be activated by a fluid, such as water, hydrocarbons, cement, drilling mud, or the like, or any suitable combination thereof. Alternatively, or additionally, the swellable medium may be adapted to be activated by heat, pressure or the like.

The swellable medium may comprise an elastomer, such as rubber or the like.

The sealing assembly may further define fluid ports adapted to permit fluid to be communicated to and from the flow path. Fluid ports may be disposed on either side of the swellable medium to thus permit fluid communication past said swellable medium. At least one fluid port may be defined by a bore extending through the wall of the sleeve. Alternatively, or additionally, at least one fluid port may be defined between the sleeve and base pipe. For example, at least one port may be defined between an open end of the sleeve and an outer surface of the base pipe. In this arrangement the at least one port may be generally annular in form. In a preferred embodiment, a first fluid port may be defined between one end of the sleeve and the outer surface of the base pipe, and a second fluid port may be defined between an opposite end of the sleeve and the outer surface of the base pipe, wherein the flow path extends between the first and second ports.

The sleeve may be concentrically mounted on the base pipe. Alternatively, the sleeve may be eccentrically mounted on the base pipe.

The sealing assembly may further comprise a support assembly adapted to mount and support the sleeve on the base pipe. A single support assembly may be provided, and may partially or completely extend along the axial length of the sleeve. In embodiments of the invention a plurality of support assemblies may be provided and may be axially distributed along the length of the sleeve. In one embodiment, a support assembly may be provided at axially opposing ends of the sleeve. A further support assembly may be provided intermediate the ends of the sleeve.

The support assembly may be freely disposed between the sleeve and the base pipe to therefore define a spacer therebetween. Alternatively, the support assembly may be secured to at least one of the sleeve and base pipe. The support assembly may be releasably secured to at least one of the sleeve and base pipe, and preferably releasably secured to at least the base pipe. This arrangement may advantageously permit the sleeve to be mounted on an existing base pipe. The support assembly may be releasably secured by screwing, bolting, interengagement, interference fitting, clamping or the like. The use of securing or fixing arrangements which can be operated without provision of specialised equipment or skilled personnel offers the advantage that the sealing assembly may be mounted on base pipe by operators on-site in response to locally identified requirements.

Alternatively, the support assembly may be permanently secured to at least one of the sleeve and base pipe, for example by welding, integrally forming, clamping or the like.

The support assembly may comprise a support member, such as a rib, extending between the sleeve and the base pipe. The support member may extend through or across the flow path, or across at least one fluid port providing fluid communication into the flow path. The support assembly may comprise a plurality of support members which may be circumferentially distributed between the sleeve and base pipe. The support member may directly engage at least one of the sleeve and base pipe. Alternatively, the support assembly may comprise at least one mounting element, wherein the support member engages at least one of the sleeve and base pipe via a mounting element. The mounting element may comprise a ring adapted to be mounted on one of the sleeve and base pipe.

In one embodiment the support assembly may comprise a first mounting element adapted to be mounted on the sleeve and a second mounting element adapted to be mounted on the base pipe, and at least one support member extending between the first and second mounting elements. The first and second mounting elements may be adapted to be releasably secured to the sleeve and base pipe, respectively. In a preferred arrangement the mounting elements may be adapted to be releasably secured by a clamping arrangement, such as by grub screws. This arrangement advantageously eliminates the requirement to penetrate the sleeve and base pipe which may establish a leak path.

The sleeve may be rigidly mounted relative to the base pipe such that relative movement therebetween is not permitted.

Alternatively, the sleeve may be adapted to be non-rigidly or releasably mounted relative to the base pipe such that relative movement therebetween is permitted. This arrangement advantageously permits the base pipe to be reciprocated relative to the sleeve to, for example, jar the sleeve and assist to unstick or assist passage of the sealing assembly from or through a tight spot within a well bore as the sealing assembly is run into the bore. Additionally, permitting the base pipe to be moveable relative to the sleeve will enable the base pipe, and any associated tubing string, to be moved after the sealing assembly has established a seal. This may therefore allow manipulation of the base pipe and associated tubing string during a cementing operation, for example, which may be desirable to assist in the uniform flow of cement within the annulus.

The sleeve may be adapted to be axially slidably mounted or alternatively, or additionally, rotatably mounted relative to the base pipe. The sleeve may be adapted to slide axially on the base pipe between axial limits defined on the base pipe. At least one axial limit may be defined by a connector disposed on an end of the base pipe to permit the base pipe to be connected to a tubing string. Alternatively, or additionally, at least one axial limit may be defined by a collar mounted on the base pipe.

The sealing assembly may comprise a band of swellable medium disposed on the sleeve. The band may continuously extend around the outer surface of the sleeve or alternatively may extend discontinuously. In one embodiment a plurality of bands of swellable medium may be provided and disposed axially along the sleeve. The bands may be directly adjacent or spaced apart at regular or irregular intervals. The bands may comprise the same swellable material, or alternatively different swellable material. For example, at least one band may comprise a swellable material adapted to be activated by water, and at least one band may comprise a swellable material adapted to be activated by hydrocarbons.

The sealing assembly may further comprise a swellable medium disposed inside the sleeve. The swellable medium within the sleeve may be adapted to establish a seal in the flow path. The swellable medium disposed both outside and inside the sleeve may be of the same material, or alternatively of different materials. The swellable medium disposed both outside and inside the sleeve may be adapted to swell at the same rate, or alternatively different rates. In one embodiment the swellable medium inside the sleeve may be adapted to swell at a slower rate that the swellable medium disposed on the outer surface of the sleeve. In this arrangement the outer swellable medium may be permitted to establish a seal within a bore while allowing flow through the flow path, wherein the flow path may be subsequently sealed by the inner swellable medium.

The swellable medium may be disposed on an inner surface of the sleeve, or alternatively, or additionally on an outer surface of the base pipe.

The sleeve may be adapted to be mounted on a plurality of base pipes.

A plurality of sleeves may be adapted to be mounted on a single base pipe.

The base pipe upon which the sleeve is mounted may form part of the sealing assembly of the present invention.

The sealing assembly may be adapted to provide downhole mechanical support. For example, the sealing assembly may be adapted to support the base pipe, and any associated tubing string, for example, within a wellbore. In one embodiment the sealing assembly may be adapted to function as a tubing hanger. In this arrangement the sealing assembly may be adapted to be located within a wellbore, such as within a lower end of an existing tubing string, and the swellable medium permitted to swell to engage an inner surface of the wellbore to thus provide a support or hanger for the base pipe. The flow path may provide fluid communication across the established support of hanger which may be beneficial in permitting annulus fluid to be displaced during a subsequent cementing operation.

According to a second aspect of the present invention, there is provided a downhole sealing assembly comprising:

a base pipe; and

a sleeve mounted on the base pipe and comprising a swellable medium, a flow path being defined between the base pipe and the sleeve.

According to a third aspect of the present invention, there is provided a method of establishing a downhole seal, said method comprising the steps of:

providing a base pipe;

mounting a sleeve on the base pipe to define a flow path therebetween, wherein the sleeve comprises a swellable medium;

running the base pipe into a wellbore; and

causing the swellable medium to swell to establish a seal.

The swellable medium may establish a seal against a wall of the wellbore.

The method may comprise the step of locating the sleeve at a desired location in the wellbore. Furthermore, the method may comprise the step of determining the desired location, for example by performing wellbore logging, which logging may be performed prior to or alternatively or additionally during the step of running the base pipe into the wellbore.

The method may comprise the step of coupling the base pipe to a tubing string and running the base pipe into the wellbore on the tubing string.

The method may comprise the step of mounting a plurality of sleeves on the base pipe.

The method may comprise the step of providing a plurality of base pipes and mounting at least one sleeve on each base pipe, and subsequently running the base pipes into the wellbore. The plurality of base pipes may be coupled to each other, either directly or indirectly via intermediate tubular members.

The swellable medium may be caused to swell by exposure to an activator, such as water, hydrocarbons, heat pressure or the like, or any suitable combination thereof. The swellable medium may be caused to swell once the desired depth is achieved. Alternatively, the swellable medium may be caused to swell during deployment into the wellbore and prior to reaching the required depth.

The method may further comprise the step of flowing cement into a wellbore and permitting the cement to flow through the flow path defined between the sleeve and the base pipe. Accordingly, a combined seal may be established between the base pipe and the wall of the wellbore, including the swellable medium and the cement. The swellable medium may provide additional sealing assurance to accommodate any possible failure or reduction in the sealing integrity of the cement. The cement may be flowed into the wellbore prior to the swellable medium fully establishing a seal. Preferably, the swellable medium is adapted to fully establish the seal before the cement cures. This arrangement therefore permits the swellable medium to displace the cement in order to establish the seal.

In one embodiment the base pipe may comprise a cement shoe, or at least a portion of a cement shoe.

According to a fourth aspect of the present invention, there is provided a method of completing a wellbore, said method comprising the steps of:

providing a tubing string;

mounting at least one sleeve on an outer surface of the tubing string to define a flow path therebetween, wherein the sleeve comprises a swellable medium;

running the tubing string into a wellbore;

causing the swellable medium to swell; and

flowing cement into the annulus formed between the tubing string and a wall of the wellbore, wherein cement flows through the flow path.

The tubing string may comprise a casing tubing string, liner tubing string or the like, or any suitable combination thereof.

According to a fifth aspect of the present invention, there is provided a cement shoe comprising:

a tubular body adapted to be mounted on a lower end of a tubing string;

a sleeve including a swellable medium mounted on the tubular body; and

a flow path defined between the tubular body and the sleeve.

According to a sixth aspect of the present invention, there is provided a downhole support assembly including a sleeve comprising a swellable medium and adapted to be mounted on a base pipe and define a flow path therebetween.

In use, the base pipe supporting the sleeve may be positioned within a bore, and the swellable medium activated to swell to engage an inner surface of the bore to thus secure and support the base pipe within the bore.

The support assembly may be adapted to support the base pipe and any associated tubing string. In one embodiment the support assembly may be adapted to function as a tubing hanger.

The flow path may provide fluid communication across the established support or hanger which may be beneficial in permitting annulus fluid to be displaced during a subsequent cementing operation.

According to a seventh aspect of the present invention, there is provided a method of supporting a tubular body within a bore, said method comprising the steps of:

mounting a sleeve comprising a swellable medium on the tubular body to define a flow path between the sleeve and the body;

running the tubular body into a bore; and

activating the swellable medium to engage a wall of the bore.

The form and function of the components of the sealing assembly defined above in connection with the first aspect may be applied within or in combination with the invention defined by the second to seventh aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspect of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation of a sealing assembly in accordance with an embodiment of aspects of the invention;

FIG. 2 is a longitudinal cross-sectional view of the sealing assembly of FIG. 1;

FIG. 3 is an enlarged view of a support member portion of the sealing assembly of FIG. 1;

FIG. 4 is a diagrammatic representation of the sealing assembly of FIG. 1 shown in use at one location within a wellbore;

FIG. 5 is a diagrammatic representation of the sealing assembly of FIG. 1 shown in use at an alternative location within a wellbore and forming part of a cement shoe;

FIG. 6 is a lateral cross-sectional view of a sealing assembly according to an alternative embodiment of the present invention;

FIG. 7 is a lateral cross-sectional view of a further alternative embodiment of the present invention;

FIG. 8 is a lateral cross-sectional view of another alternative embodiment of the present invention; and

FIG. 9 is a diagrammatic representation of the sealing assembly of FIG. 1 functioning as a tubing hanger.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is first made to FIGS. 1 and 2 of the drawings in which there is shown a sealing assembly, generally identified by reference numeral 10, in accordance with an embodiment of the present invention, wherein FIG. 2 is a longitudinal cross-sectional view through the assembly 10. The sealing assembly 10 comprises a sleeve 12 which is mounted on a base pipe 14, which in the embodiment shown is a pup joint length of casing. The sleeve 12 is concentrically mounted on the base pipe 14 via support assemblies or caps 16 which are positioned at axially opposed ends of the sleeve 12. The support caps 16 will be described in further detail below.

An annular flow path 18 (FIG. 2) is defined between the outer surface of the base pipe 14 and an inner surface of the sleeve 12. Axially opposed annular ports 20 are defined between the open ends of the sleeve 12 and the outer surface of the base pipe 14, wherein the ports 20 permit fluid communication to and from the annular flow path 18. A plurality of circumferential bands of swellable material 22 are distributed along the length of the outer surface of the sleeve 12. The swellable material is adapted to swell upon exposure to a particular activator, such as water, hydrocarbons, drilling mud, cement of the like. Each band 22 may be formed of the same material, or alternatively the bands 22 may be formed of different materials, depending upon user requirements. For example, adjacent bands 22 may contain swellable material which is adapted to be activated by water and hydrocarbons respectively.

In use, the base pipe 14 may be connected at either end thereof to a tubing string (now shown) via end connectors 24 and subsequently run into a wellbore (not shown) to position the sleeve 12 at a desired depth. When the swellable material within the bands 22 is exposed to a particular activator, the material will be caused to swell and therefore radially expand to fill the annulus between the sleeve 12 and the wall of the wellbore within which the sealing assembly 10 is located. Accordingly, the sealing assembly 10 may be adapted to establish a seal against a particular section within a wellbore. The flow path permits fluid communication past the seal established by the bands 22. Additionally, the flow path 18 will permit fluids resident in the wellbore to be displaced therethrough when the sealing assembly 10 is run into the wellbore. This may therefore assist to prevent the occurrence of hydraulic locking, particularly when the bands of swellable material describe a diameter similar to the wellbore and provide little if any external clearance. Use of the sealing assembly 10 will be described in further detail below.

Reference is now additionally made to FIG. 3 of the drawings in which there is shown an enlarged view of one of the support caps 16 of the sealing assembly 10. Each support cap 16 comprises a first mounting element or ring 26 which is mounted on the outer surface of the base pipe 14, and a second mounting element or ring 28 which is mounted on the outer surface of the sleeve 12 at an end thereof. A plurality of support members or ribs 30 extend between the first ring 26 and second ring 28 to concentrically mount the sleeve 12 on the base pipe 14. The support ribs 30 are evenly circumferentially distributed around the support assembly 16 and the spaces defined between each adjacent rib 30 collectively define the annular port 20 which allows or permits fluid communication to and from the annular flow path 18.

The second ring 28 defines a plurality of circumferentially distributed screw holes 32 which permit the second mounting ring 28 and thus the support cap 16 to be secured to the sleeve 12 via suitable screws. In a preferred embodiment the screws are grub screws and are adapted to clamp against the outer surface of the sleeve 12.

The first ring 26 also comprises a plurality of circumferentially distributed screw holes 34 which permit the ring 26 and thus support assembly 16 and sleeve 12 to be secured to the base pipe 14 via suitable screws. In one embodiment the screws are grub screws adapted to clamp against the outer surface of the base pipe 14. This arrangement is particularly advantageous in that penetration of the base pipe 14 is not required and as such a leak path is not established, and that welding equipment and the like need not be provided or used to secure the support assembly 16 to the sleeve 12 and the support assembly 16 to the base pipe 14.

In embodiments of the invention, the sleeve 12 may be secured on the base pipe 14 in the manner described above. However, in alternative embodiments the sleeve 12 may remain unsecured to the base pipe 14 such that the sleeve 12 may be permitted to slide axially. In this arrangement the sleeve 12 may be limited to slide on the base pipe 14 between the connectors 24 (FIGS. 1 and 2) which will be engaged by the respective first rings 26 of each support cap 16. This sliding arrangement advantageously permits the base pipe 14 to be reciprocated relative to the sleeve 12 to, for example, jar the sleeve 12 and assist to unstuck or assist passage of the sealing assembly 10 from or through a tight spot within a wellbore.

Reference is now made to FIG. 4 of the drawings in which the sealing assembly 10 first shown in FIG. 1 is shown diagrammatically in use within a subterranean wellbore 36. In the example shown the wellbore 36 extends through a first earth formation 38 which predominately contains hydrocarbons, such as oil, and a second earth formation 40 which predominately contains water.

Conventionally, a tubing string such as a liner string would be run into a wellbore, similar to wellbore 36, and subsequently cemented in place to therefore prevent fluids from different earth formations, such as formations 38, 40 from entering the annulus between the liner tubing and the bore wall. Perforations may then be formed within the liner string using explosive charges to open a preferred formation, such as formation 38, to the string. However, on many occasions the sealing integrity of the annulus cement is inefficient or is reduced over time, for example, by the formation of cracks, flow channels, micro-annuli and the like. Such flow passages and the like may permit fluid from a closed formation, such as formation 40 to migrate along the annulus towards the open formation 38 and subsequently be produced to surface, which may be undesirable. In one use of the present invention, as shown in FIG. 4, the sealing assembly 10 seeks to address this problem.

Specifically, the sealing assembly 10 incorporating the sleeve 12 and base pipe 14 is coupled to a liner string 42 via the connectors 24. The liner string 42 may then be run into the wellbore 36 to locate the sealing assembly 10 adjacent formation 40. The location of the formation 40 may be determined by use of conventional logging techniques such as open hole logging, logging while drilling or the like.

The sealing assembly 10, and in particular the bands of swellable material 22, may be of a diameter equal to the diameter of the drill bit which was used to drill the wellbore section 36. Thus, only a relatively limited degree of swelling, and a limited time, is required to obtain a sealing contact between the swellable material 22 and the wellbore wall. Disadvantages normally associated with such tight sizing are avoided by various features of the assembly. Fluid displaced by the descending tubing string may pass through the flow path 18 between the sleeve 12 and the base pipe 14, and does not have to negotiate the small gap between the sealing assembly 10 and the wellbore wall. Also, the swellable material 22 is elastomeric and has a degree of compliancy. Furthermore, if the swellable material 22 is worn or damaged by contact with the bore wall such wear and damage will tend to have little if any effect on sealing performance as adjacent swellable material will tend to swell into and occupy areas of damage or wear. The thickness of swellable material provided in the assembly will also be selected to provide an excess of swelling capacity such that, for example, a loss of some material through wear, will not compromise the assembly's sealing capability.

The bands 22 of swellable material may then be activated to swell to engage the bore wall and thus seal the formation 40. The swellable material may be adapted to swell when exposed to water within the well bore 36, and the swelling process may begin while the liner string 42 incorporating the sealing assembly 10 is being run into the well bore 36. Accordingly, the bands of sealing material 22 may be almost entirely swollen to the desired sealing diameter when total depth is achieved, thus further decreasing the swelling and sealing time at the required depth.

The annulus 44 formed between the wall of the bore 36 and the outer surface of the liner string 42 may be filled with cement 46 in a conventional manner, wherein the flow path 18 defined between the sleeve 12 and base pipe 14 permits the cement to bypass the seal established by bands 22 and therefore fill the portion of the annulus 44 located above the sealing assembly 10.

Accordingly, the sealing assembly 10 may be used in combination with a conventional cementing operation to assure that sufficient sealing integrity will be achieved, particularly at locations, such as at the location of formation 40 where conventional cement sealing is known to be ineffective or inefficient. Additionally, annulus sealing at the desired location utilising the sealing assembly 10 of the present invention is not dependent upon the cement 46 making a sufficient bond with the borewall. Furthermore, any movement of the sealing assembly 10 relative to the borewall after a seal is initially established will be accommodated by further swelling of the bands 22 to thus continually maintain a seal.

It should be noted that subsequent to the cementing process, cement will be cured to seal the flow path 18. In this respect, the inner surface of the sleeve 12 and outer surface of the base pipe 14 will provide a clean surface to ensure bonding of the cement thereto. Additionally, thermal expansion of the base pipe 14 and sleeve 12 should occur at substantially the same rate and as such should not impart significant stresses into the cement which may otherwise cause damage thereof and create cracks and flow paths to therefore reduce the integrity of the cement seal.

Once the liner string 42 is adequately sealed within the wellbore 36, perforations 48 may be formed through the wall of the liner string 42 and through the annulus cement 44 at the location of formation 38 to therefore permit production of hydrocarbons.

It should be noted that any number of sealing assemblies 10 may be positioned axially along the length of the tubing string 42 in order to provide sealing assurance at any desired location within the wellbore 36.

Reference is now made to FIG. 5 of the drawings in which the sealing assembly 10 is shown in use at an alternative location within a wellbore 36 a and forming part of a cement shoe 50. The cement shoe 50 is mounted on a lower end of a tubing string 52, such as a casing string, and as such is adapted to be located within the bottom of the bore 36 a. The cement shoe 50 comprises a plurality of ports 54 which permit cement 46 to exit the tubing string 52 and cement shoe 50 and flow into the annulus 44 a.

The bands of swelling material 22 may be activated to swell to engage the wall of the bore 36 a and thus establish a seal, while the flowpath 18 formed between the base pipe 14 and sleeve 12 permits cement 46 to bypass the established seal and thus fill the annulus 44 a positioned above the sealing assembly 10.

Conventionally, following a cementing operation at least a portion of the cement shoe 50 remains filled with cement which will subsequently cure. Accordingly, if the wellbore 36 a is to be advanced, the cured cement within the cement shoe 50 will need to be drilled through using an appropriate drilling assembly. Accordingly, the cement shoe 50 and surrounding annulus 44 a, cement 46 and formation 54 will be exposed to vibration and other mechanical loading as a result of the drilling process. However, the presence of the sealing assembly 10 forming part of the cement shoe 50 will assist to ensure that sealing integrity within the annulus 44 a will be maintained.

A lateral cross-sectional view of a sealing assembly, generally identified by a reference numeral 60, in accordance with an alternative embodiment of the present invention is shown in FIG. 6, reference to which is now made. The sealing assembly 60 is similar to sealing assembly 10 first shown in FIG. 1 and as such comprises a base pipe 62 upon which is mounted a sleeve 64 to define a flow path 66 therebetween. A swellable material 68, which may be provided in a band arrangement as shown in the embodiment of FIG. 1, is mounted on the outer surface of the sleeve 64.

The sleeve 64 is supported on the base pipe 62 via a plurality of ribs 70 which extend between the outer surface of the base pipe 62 and an inner surface of the sleeve 64. The ribs 70 may be secured, either releasably or permanently, to either one of the base pipe 62 and sleeve 64. Additionally, the ribs 70 may extend at least partially along the length of the sleeve 64.

A further alternative embodiment of a sealing assembly according to the present invention is shown in FIG. 7, reference to which is now made. The sealing assembly, generally identified by reference numeral 80, is similar to the assembly 60 shown in FIG. 6, and as such comprises a base pipe 82 which supports a sleeve 84 via ribs 90, wherein a flow path 86 is established between the base pipe 82 and sleeve 84. A swellable material 88 is disposed on the outer surface of the sleeve 84. Additionally, a further swellable material 92 is disposed on the inner surface of the sleeve 84. Accordingly, the swellable material 92 may be activated to swell to seal the flow path 86. In embodiments of the invention, the swellable material 92 on the inner surface of the sleeve 84 may be adapted to swell at a different rate than the outer swellable material 88. For example, the inner swellable material 92 may be adapted to swell at a slower rate than the outer material 88. In this arrangement, material 88 may swell to establish a necessary seal against a bore wall, while the flow path 86 remains open to allow fluid to bypass the established seal. The inner material 92 may subsequently fill the flow path 86 and therefore prevent further fluid communication thereacross.

It should be noted that while the sleeve 84 is shown mounted on the base pipe 82 via ribs 90, the sleeve 84 may alternatively be mounted via a support cap 16 first shown in FIG. 1.

Reference is now made to FIG. 8 of the drawings in which there is shown a lateral cross-sectional view of a sealing assembly, generally identified by reference numeral 100, in accordance with a further alternative embodiment of the present invention. The sealing assembly 100 comprises a base pipe 102 which supports an outer sleeve 104 via ribs 110, wherein the base pipe 102 and outer sleeve 104 collectively define a flow path 106. A swelling material 108 is mounted on the outer surface of the sleeve 104. Additionally, a swellable material 112 is mounted on an outer surface of the base pipe 102. The swellable material 112 may therefore swell to seal the flow path 106.

It should be noted that a support cap arrangement 16 as shown in FIG. 1 may alternatively be used to support the sleeve 104 on the base pipe 102 of the sealing assembly 100.

Reference is now made to FIG. 9 of the drawings in which a sealing assembly according to an embodiment of the present invention is shown in use as a tubing hanger. The sealing assembly/tubing hanger, generally identified by reference numeral 120, is generally similar to any of the previously described sealing assemblies 10, 60, 80, 100 described above, and as such comprises a sleeve 122 which is mounted externally of a base pipe 124 to define a flow path 126 therebetween. Bands of swellable material 128 are mounted on an outer surface of the sleeve 122. In the embodiment shown the base pipe 124 forms part of a lower tubing string 130.

In use, the sealing assembly/tubing hanger 120 is adapted to secure the lower tubing string 130 to a lower end portion of an upper tubing string 132. In use, the upper tubing string 132 may be mounted within a first wellbore section 134 and subsequently cemented in place. A second wellbore section 136 may then be drilled and the lower tubing string 130 may be run into the second wellbore section 136 such that the upper end of the lower tubing string 130 overlaps with the lower end of the upper tubing string 132. The bands of swellable material 128 may be activated to swell to engage the inner surface of the upper tubing string 132 to therefore secure the lower tubing string 130 relative to the upper tubing string 132. The lower tubing string 130 may subsequently, or simultaneously, be cemented in place within the second wellbore section 136. Advantageously, the flow path 126 may permit fluids to be displaced from the second wellbore section 136 during the cementing operation.

Although not shown in FIG. 9, the flow path 126 may incorporate a further swellable material which may be adapted to swell to subsequently seal the flow path 126, for example after the lower tubing string 130 has been cemented in place.

It should be understood that the embodiments described above are merely exemplary and that various modifications may be made thereto without departing from the scope of the present invention. For example, the swellable material disposed on the outer surface of the sleeve may be provided as a continuous band. Additionally, the sleeve may be supported on the base pipe by any suitable support means which permit a flow path to be maintained. Furthermore, the sleeve is shown in the various embodiments being concentrically mounted on the base pipe. However, in alternative embodiments the sleeve may be eccentrically mounted. One or more collars may be mounted on the base pipe which may be used to limit axial sliding of the sleeve thereon.

The sealing assembly may be utilised at any location within a wellbore where a seal is required to be established against a bore wall. Additionally, although the embodiments described above demonstrate the sealing assembly being used in combination with a cementing process, it should be understood that the sealing assembly is not adapted exclusively for use as such.

Furthermore, the base pipe may comprise any downhole tubular, such as a casing tubular, production tubular, drilling tubular, liner tubular or the like. 

1. A downhole sealing assembly including a sleeve comprising a swellable medium wherein the sleeve is adapted to be mounted on an outer surface of a base pipe to define a flow path between the sleeve and the base pipe.
 2. The assembly of claim 1, wherein the swellable medium is adapted to swell to provide a seal within an annulus formed between the sleeve and a surrounding bore wall.
 3. The assembly of claim 2, adapted to maintain the flow path following formation of said seal.
 4. The assembly of claim 1, wherein the swellable medium is adapted to swell during deployment into a bore.
 5. The assembly of claim 1, wherein the flow path is adapted to permit resident or ambient wellbore fluids to be displaced therethrough as the sealing assembly is run in-hole.
 6. The assembly of claim 1, wherein the flow path is adapted to permit cement to cure therein, such that the cement provides a seal across the sealing assembly.
 7. The assembly of claim 1, adapted to be utilised adjacent, in combination with or part of a cement shoe.
 8. The assembly of claim 1, comprising a base pipe.
 9. The assembly of claim 8, wherein the base pipe comprises a downhole tubular comprising at least one of: a casing tubular, liner tubular, drilling tubular, drilling collar, cement shoe and coiled tubing.
 10. The assembly of claim 8, wherein the base pipe is adapted to define or be coupled to and form part of a tubing string to be run downhole into a bore.
 11. The assembly of claim 1, wherein the swellable medium is adapted to swell at least in part by volumetric expansion thereof.
 12. The assembly of claim 1, wherein the swellable medium is adapted to swell upon exposure to an activator.
 13. The assembly of claim 1, wherein the swellable medium comprises an elastomer.
 14. The assembly of claim 1, comprising a support assembly adapted to mount the sleeve on the base pipe.
 15. The assembly of claim 14, wherein the support assembly is adapted for retrofitting the sleeve to an existing base pipe.
 16. The assembly of claim 14, wherein the support assembly is adapted for mounting the sleeve on the base pipe without penetrating the base pipe.
 17. The assembly of claim 14, wherein a support assembly is provided at each axial end of the sleeve.
 18. The assembly of claim 14, wherein a support assembly is provided intermediate the axial ends of the sleeve.
 19. The assembly of claim 1, wherein the sleeve is adapted to be axially fixed relative to the base pipe.
 20. The assembly of claim 1, wherein the sleeve is adapted to be axially movable relative to the base pipe.
 21. The assembly of claim 20, wherein the axial movement of the sleeve relative to the base pipe is limited by at least one stop.
 22. The assembly of claim 1, wherein the sleeve is adapted to be rotationally fixed relative to the base pipe.
 23. The assembly of claim 1, wherein the sleeve is adapted to be rotationally movable relative to the base pipe.
 24. The assembly of claim 1, comprising a band of swellable medium disposed on the sleeve.
 25. The assembly of claim 24, comprising a plurality of bands of swellable medium disposed axially along the sleeve.
 26. The assembly of claim 25, wherein the bands are spaced apart.
 27. The assembly of claim 25, wherein the bands comprise the same swellable material.
 28. The assembly of claim 25, wherein the bands comprise different swellable materials.
 29. The assembly of claim 28, wherein at least one band comprises a swellable material adapted to be activated by water, and at least one band comprises a swellable material adapted to be activated by hydrocarbons.
 30. The assembly of claim 1, comprising a swellable medium disposed outside the sleeve.
 31. The assembly of claim 1, comprising a swellable medium disposed inside the sleeve.
 32. The assembly of claim 31, wherein the swellable medium disposed inside the sleeve is adapted to establish a seal in the flow path.
 33. The assembly of claim 30, wherein swellable media disposed outside and inside the sleeve have different swelling characteristics.
 34. The assembly of claim 33, wherein the swellable medium disposed inside the sleeve is adapted to swell at a slower rate that the swellable medium disposed outside the sleeve.
 35. The assembly of claim 1, wherein the assembly is adapted to provide downhole mechanical support for at least the base pipe.
 36. The assembly of claim 35, wherein the assembly is adapted to function as a tubing hanger.
 37. (canceled)
 38. A method of establishing a downhole seal, said method comprising the steps of: providing a base pipe; mounting a sleeve on an outer surface the base pipe to define a flow path therebetween, wherein the sleeve comprises a swellable medium; running the base pipe into a wellbore; and causing the swellable medium to swell to establish a seal.
 39. The method of claim 38, wherein the swellable medium establish a seal against a wall of the wellbore.
 40. The method of claim 38, wherein the swellable medium is caused to swell by exposure to an activator.
 41. The method of claim 38, further comprising flowing cement into a wellbore and permitting the cement to flow through the flow path defined between the sleeve and the base pipe.
 42. The method of claim 41, comprising permitting the cement to cure in and seal the flow path.
 43. A method of completing a wellbore, said method comprising the steps of: providing a tubing string; mounting at least one sleeve on an outer surface of the tubing string to define a flow path therebetween, wherein the sleeve comprises a swellable medium; running the tubing string into a wellbore; causing the swellable medium to swell; and flowing cement into the annulus formed between the tubing string and a wall of the wellbore, wherein cement flows through the flow path.
 44. A cement shoe comprising: a tubular body adapted to be mounted on a lower end of a tubing string; a sleeve including a swellable medium mounted on an outer surface of the tubular body; and a flow path defined between the tubular body and the sleeve.
 45. A downhole support assembly including a sleeve comprising a swellable medium and adapted to be mounted on an outer surface of a base pipe and define a flow path therebetween.
 46. A method of supporting a tubular body within a bore, said method comprising the steps of: mounting a sleeve comprising a swellable medium on an outer surface of the tubular body to define a flow path between the sleeve and the body; running the tubular body into a bore; and activating the swellable medium to engage a wall of the bore. 